I was reading about the types of diodes, including those that can be used to generate microwaves, and I found myself confused about the material I found on it. This link discusses the differences between three kinds of diodes, but I'm simply having trouble interpreting these diagrams that I come across, because I'm unclear about what p+ and n+ mean vs p and n in a diagram. I think that p and n are used to represent positively and negatively doped semiconductor material, but I'm unclear with these diagrams that use pluses and minuses in addition to n and p.
Most semiconductor device processes have a few doping levels available for the designer to use. Instead of working with the actual concentrations, it's easier to work with p+ vs. p to say it has more acceptors. N+ will similarly have more donors.
It's very common in semiconductor physics to go even further and use: n--, n-, n, n+, n++ or p--, p-, p, p+, p++ to talk about doped regions.
Eg. We could be working with an extremely P lowly doped substrate (p--) in which you have a pwell (p-) and the contact to the pwell is made with a highly doped diffusion region (p+).